Not applicable.
This invention relates to the incorporation of a drying oil and a copper containing preservative system into wood products, which may include lumber and plywood, and into wood and agricultural based composite products. Wood based composite products can include products such as oriented strandboard, medium density fiberboard, fiberboard, hardboard, and particle board. The invention also relates to the method of manufacturing wood based composite products whereby a drying oil and a wood preservative composition are added to the wood furnish (defined as wood strands, chips, particles, flakes and fiber), plywood (whether in the form of separate plies or a bound sheet), or solid wood prior to or after drying. Where a wood furnish or separate wood plies are treated, the wood is then formed and pressed into a finished board or panel product.
The production of wood based composite panel products has increased dramatically in recent years. Oriented strandboard (OSB) production exceeded that of plywood in the Year 2000. In order to continue this new growth, additional uses for OSB need to be developed. Common applications for these products include roof sheathing, wall sheathing, flooring, structural insulated panels and engineered wood components such as I-joists. With the ever-expanding production capacity of wood based composites there is a critical need to find additional uses.
The use of medium density fiberboard and hardboard panel products likewise has increased dramatically over the last couple decades. However, these products are typically used in interior applications where attack from insects or decay fungi is limited and dimensional stability is not of great concern. The market for these types of materials is fairly well developed. To maintain market share and increase production it will be necessary to develop new products that can withstand exterior environments.
The expansion of wood fiber, particle and flake based composites into certain construction applications is hindered by limitations in the physical and mechanical properties of the manufactured panels, in particular excessive water absorption and propensity to swell, but also by their susceptibility to attack by biological agents such as decay fungi and termites.
Chemical preservatives and water repellent treatments are available for solid lumber and plywood. Such chemical treatments are applied to lumber, millwork, wood plies, and so forth using vacuum pressure processes to ensure uniform distribution of the active ingredients throughout the wood components. Treated woods find application in the construction of residential housing and commercial buildings.
Historically, attempts to incorporate chemical treatments into wood based composites using similar technology have failed for economic reasons or more commonly because of technical problems associated with irreversible and excessive swelling of the treated panels and severe loss of structural integrity.
The development of an economically viable preservative/water repellent treatment for solid wood, plywood, and wood based composites with minimal or no impact on board structural properties, would be desirable to the industry and consumers.
The development of such products would have a significant impact upon the forest resources of North America as well as the world. Solid wood or a formed panel product that has been treated to resist biological action and is inherently stable to resist water will significantly increase the service life of the final wood product. Hence replacement of damaged, decayed, or destroyed panels will be less frequent. Therefore, more solid wood and wood fiber can be channeled to new construction and not the replacement market. This will limit the stress on the forest resources of North America, which have been shrinking over the last two decades due to land being tied up in xe2x80x9cnaturalxe2x80x9d status, which cannot be harvested.
U.S. Ser. No. 09/550,027, filed Apr. 14, 2000, now U.S. Pat. No. 6,565,540, entitled: Dimensionally Stable Wood Composites And Methods For Making Them, discloses treated wood composites and their ingredients and manufacture. The latter application is incorporated by reference in its entirety.
PCT patent application WO 92/19429, published Nov. 12, 1992, in Example 2, describes a method of treating an article of prepared wood by immersing it for 20 minutes in a bath of 180xc2x0 C. linseed oil containing a drier (siccative) of 0.07% lead, 0.003% manganese and 0.004% calcium and 0.3% copper naphthenates and 0.03 zinc naphthenates as an insecticide and fungicide.
U.S. Pat. Nos. 5,607,633, 5,719,301, and 6,277,310 describe bonding composite panels such as oriented strand board, particle board, plywood, MDF, hardboard, and similar panels, using a material such as linseed oil, which may be modified to provide bonding characteristics.
Fojutowski, A.; Lewandowski, O, Zesz. Probl. Postepow Nauk Roln. No. 209: 197-204 (1978), describes fungicides comprising fatty acids with copper compounds, applied by dipping hardboard heated to 120xc2x0 C. into a bath of the fungicide, also maintained at 120xc2x0 C.
Japanese Patent Application 08-183,010 JP, published in 1996, describes a modified wood claimed to have mildew-proofing and antiseptic properties and ant-proofing properties, made by treating wood with a processing liquid containing a composite multivalent metal (one example of which is copper) salt and linseed oil or another liquid hardening composition. The abstract states that the composite multivalent metal salt is strongly fixed within the material so as to let the composite multivalent metal salt give antibacterial properties, antiseptic properties, ant-proofing properties, water repellency and strength to wood.
U.S. Pat. No. 3,837,875 describes as a composition for cleaning, sealing, preserving, protecting and beautifying host materials such as wood a mixture of boiled linseed oil, turpentine, pine oil, a dryer and atomized metallic copper with the copper being present in a ratio of about 28 parts per million.
Feist, William C.; Mraz, Edward A., Forest Products Lab Madison Wis., Wood Finishing: Water Repellents and Water-Repellent Preservatives. Revision, Report Number-FSRN-FPL-0124-Rev (NTIS 1978) discloses preservatives containing a substance that repels water (usually paraffin wax or related material), a resin or drying oil, and a solvent such as turpentine or mineral spirits. Addition of a preservative such as copper naphthenate to the water repellent is asserted to protect wood surfaces against decay and mildew organisms.
Soviet Union Patent No. SU 642166 describes a wood surface staining and preservation treatment, carried out by impregnating wood with an aqueous copper salt solution, followed by thermal treatment in boiling drying oil containing 8-hydroxyquinoline dye. The copper salt and the dye form a complex which is stated to stain and preserve the wood.
Schultze-Dewitz, G., Improvement of Beech Wood, HOLZFORSCHUNG UND HOLZVERWERTUNG Vol. 46, No. 2, 1994 pp. 34-39, states that specimens of beech wood in air-dried, green, and water-stored conditions (about 15, 120 and 150-180% moisture content, respectively) were impregnated with nine different chemicals/mixtures, and effects on the dimensional stability and physical-and mechanical properties of the wood. One of the impregnants was linseed oil varnish. All the impregnants were said to dimensional stability, and also were disclosed to improve certain properties of the wood.
Pizzi, A., A New Approach To Non-Toxic, Wide-Spectrum, Ground-Contact Wood Preservatives. Part I. Approach And Reaction Mechanisms, HOLZFORSCHUNG Vol. 47, No. 3, 1993, pp. 253-260, asserts that copper soaps, made with the carboxylic acid groups from unsaturated fatty acids of edible vegetable oils which are non-toxic (such as corn oil or sunflower oil), from resin acids of rosin which are non-toxic, and also from synthetic unsaturated polyester resins were shown in 25-year tests to have effectiveness and long-term durability as ground contact wood preservatives for use against termites and fungal attack.
One aspect of the present invention is treated wood comprising a copper based wood preservative, for example a copper ammonium acetate complex, and a drying oil. The drying oil can be, for example, a drying agricultural oil or fish oil.
The wood preservative is present in the wood in an amount effective to improve the resistance of the treated wood to at least one type of decomposition. Alternative types of decomposition contemplated here are decay, termite or other insect damage.
The drying oil is present in the wood in an effective amount to accomplish at least one useful end. One useful end is to reduce the water absorption of the treated wood. An alternative useful end is to reduce the thickness swell of the treated wood.
Another aspect of the invention is a treated wood composite comprising: a predominant proportion of wood particles; a copper based wood preservative; and a drying oil.
The wood preservative again is present in the wood composite in an amount effective to improve the resistance of the treated wood composite to at least one type of decomposition.
The presence of a copper based wood preservative with a reactive agricultural oil or fish oil has the potential to provide biological efficacy against wood biodeteriogens. (A biodeteriogen is an organism that is capable of causing biodeteriorationxe2x80x94an undesirable change in the properties of a material caused by the vital activities of living organisms.) Biodeteriogens for wood include decay fungi, termites and other insects. Complexation of the preservative with the reactive oil reduces the likelihood of leaching/depletion of the preservative in service.
The drying oil again is present in the wood in an effective amount to accomplish at least one useful end. For example, the drying oil may interact to enhance the dimensional stability or water repellency of the wood composite, and may function to reduce or eliminate the need for a separate binder resin.
Yet another aspect of the invention is a method of making treated wood composites. One step of the method is providing green wood in flaked form. Another step of the method is adding to the green wood a copper based wood preservative. The wood preservative again is added to the wood composite in an amount effective to improve the resistance of the treated wood composite to at least one type of decomposition. Another step of the method, alternatively carried out simultaneously with, before, or after the wood preservative treatment, is adding to the green wood a drying oil. The drying oil again is present in the wood composite in an effective amount to accomplish at least one useful end.
One advantage of the present method is that it allows the wood to be treated with the preservative while green, then dried once, instead of drying the wood, treating it with a water dispersion of the treating agent (thus rewetting the wood), then drying the wood a second time.
The present inventors have jointly developed a system for incorporating a copper based preservative system, for example the treatment commercially available as the COMPTEC(trademark) copper ammonium acetate complex wood treatment, in combination with drying oils functioning as described herein, into the manufacturing process for solid wood, plywood, and wood based composites.
Pertinent copper based preservatives include, for example:
alkaline (amine or ammonia) copper quats (ACQ)
ammonium/copper complex
ammoniacal copper zinc arsenate (ACZA)
bis(N-cyclohexyldiazeniumdioxy)copper
copper acetate
copper ammonium acetate complex
copper azole
copper borate
copper carbonate
copper citrate,
copper fluoride
copper fluoroborate
copper hydroxide
copper hydroxycarbonate
copper naphthenate
copper oxide
copper oxychloride
copper salt of 8-Hydroxyquinoline
copper sulfate
diethanolamine/copper complex
diethylamine/copper complex
ethanolamine/copper complex
ethylene diamine/copper complex
triethanolamine/copper complex
and combinations thereof. Many copper-based wood preservatives are known, and their use is contemplated here.
Pertinent agricultural drying oils include linseed, soybean, canola, rapeseed, sunflower, tung and castor oils and any other oils derived from agricultural sources. Pertinent fish oils, which are also drying oils, can be extracted from sardines, mackerel, codfish (including but not limited to cod-liver oil), tuna, salmon, pilchard, menhaden, and herring, as well as other species.
For composite panel products, the oil copper combination can be applied to a wet (green) or dry wood or wood furnish but is most optimally applied to green or wet wood furnish at a moisture content (MC) above the fiber saturation point (i.e. above 30% MC). The use of a green wood furnish ensures that the penetration of the preservative system into wood flakes is maximized for optimum efficacy.
In the case of solid lumber, piles, and already manufactured plywood, the copper combination is preferably applied to dry wood at a moisture content around 15-19%. The use of dry wood ensures penetration deep into the wood to maximize penetration.
The addition rate for the copper ammonium acetate complex wood treatment formulation may range from 0.5% m/m (i.e. xe2x80x9cmass-to-massxe2x80x9d or weight %) active ingredient to 5% m/m active ingredient defined on a copper ammonium acetate complex basis.
The drying oil addition rate may vary from 0.5% to 50% by weight (m/m). The lower limit of drying oil addition can alternatively be 1%, 1.25%, 2%, 2.5%, 3%, 4%, or 5% by wood weight, on the same basis. The upper limit of drying oil addition can alternatively be 50%, 40%, 30%, 25%, 20%, 15%, 14%, or 13%, or 12%, or 11%, or 10%, or 8%, or 6%, or 5% by wood weight, on the same basis. The decay and termite resistance performance of the finished panels are proportionally linked to the weight percentage of copper ammonium acetate complex wood treatment incorporated into the furnish. Similarly, improvements in water absorption and thickness swell is proportionally related to the level of oil incorporated into the matrix.
The COMPTEC(trademark) wood composite treatment and the oil are believed to be synergistic when used to treat solid wood, wood composites, or plywood. Their use in wood based composites can provide mechanical panel properties that are superior to those expected with conventional resin systems alone. The increase in mechanical properties correlates with the quantity of oil and copper ammonium acetate complex wood treatment added to the furnish or plies. Given a consistent resin loading, as the level of oil increases per given level of copper ammonium acetate complex wood treatment, the mechanical properties improve significantly. The interaction of the copper based wood treatment and oil is believed to create a secondary resin source which enhances the overall furnish to furnish (particle/flake: particle/flake) bonding in wood composites. This improves the overall mechanical properties of the finished panel.
This interaction is thought to act similarly to a chemical process known as epoxidation in which oils derived from agricultural products can be converted from liquids into either soft or hard plastic compounds. Examples of this would be bags used for blood collection and PVC plastic stabilizer for plastic piping used for plumbing. Chemically, epoxidation involves the addition of an oxygen bridge to unsaturated oil molecules via a catalytic reaction pathway. In this invention, copper ions are provided by the copper ammonium acetate complex wood treatment.
Therefore, it is hypothesized that, in the manufacture of wood based composites and plywood, especially during pressing, the active ingredients of the copper ammonium acetate complex wood treatment epoxidize the oil, creating a secondary binding agent for the wood. Using both a copper ammonium acetate complex and a drying oil, it is possible to make composite wood products using no other synthetic binding resins that are currently used by industry. These resins include phenol formaldehyde, isocyanates, and urea formaldehyde resins.
The treatment of solid wood with an oil and another copper based wood preservative is also contemplated. Copper ammonium acetate complex (COMPTEC(trademark)) and alkaline copper complex wood treatment solutions are two of many copper based formulations that are suitable for this purpose.
The treatment solutions can be emulsified using water as a carrier, the oil can be utilized as the carrier of the biocide treatment, or the oil and biocide can be applied separately, as by first treating the wood with the copper complex, then treating it with the reactive oil, which can be applied, for example, in the form of an aqueous emulsion.
The reactive oil can alternatively be formulated as part of a water repellent emulsion system that is subsequently applied to the wood, which can also include a binding resin. The copper complex, reactive oil, water repellant, and binding resin, or any subset of them can also be provided as one formulation. The inventors contemplate that if the wax emulsion and the copper complex are present in the same formulation and would otherwise tend to react prematurely, the wax emulsion will partially shield the oil from the copper in this single step emulsion. The copper and oil then will interact when the wax emulsion breaks within the wood.
The wood may be treated by pressure treatment, much like other wood treatments are applied to solid wood. One pressure treatment may be used, or a series of two or more pressure treatments may be used. More than one pressure treatment may be applied if the copper complex and reactive oil are added from separate formulations.
The copper complex and reactive oil treatments can be carried out at ambient temperature, for example 21xc2x0 C., at a lower temperature, or at an elevated temperature. For example, although the treatment temperature is not contemplated to be critical, a suitable temperature range is 0xc2x0 C.-179xc2x0 C., alternatively 0xc2x0 C.-119xc2x0 C., alternatively 0xc2x0 C.-100xc2x0 C., alternatively 0xc2x0 C.-80xc2x0 C., alternatively 0xc2x0 C.-60xc2x0 C., alternatively 0xc2x0 C.-50xc2x0 C., alternatively 0xc2x0 C.-40xc2x0 C., alternatively a lower limit of any of the preceding ranges of 15xc2x0 C.
The epoxidization process is contemplated to improve the mechanical properties of solid wood, as well as preserving it. It is hypothesized that the epoxidation process between the copper ions and reactive oil occurs, or is at least initiated, when the oil/copper treated solid wood is dried using conventional drying equipment to a moisture content appropriate for its eventual end use.
An oil/copper treated wood furnish can also be dried using conventional drying equipment to a moisture content appropriate to the type of resin system that is utilized for the specific composite product being manufactured. On the other hand, copper treated wood flakes can be first dried and then sprayed with the oil at the same time as resin and wax are applied in a conventional blender prior to forming and pressing. The moisture content of the furnish treated in this manner can range from 0.5% to 25% MC based on oven-dry weight of furnish. The dried furnish optionally may be blended with any of a vast variety of resins currently used by the composite wood industry. Such resins could include, but are not limited to liquid phenol formaldehyde (LPF), powder phenol formaldehyde (PPF), acid catalyzed PF resins (commonly known as Novolac resins), isocyanate (MDI), phenol-melamine-formaldehyde adhesives (PMF), urea formaldehyde, or combinations of those resins. Addition rates may vary from 0% to 25% resin solids depending on panel type and application.
The dry treated wood furnish is sprayed with resin and wax (and in some cases the drying oil), formed and oriented into a mat of the desired thickness and pressed to form the final panel. Mats are formed to suit the type of composite and desired end use. Formed mats are pressed under heat and pressure conditions appropriate to the final end use of the finished board. Typical press parameters include consolidation pressures ranging from 50 psi (35 N/cm2) to 650 psi (453 N/cm2), cook pressures from 0 psi (0 N/cm2) to 400 psi (280 N/cm2), and a de-gas segment. Typical press temperatures vary from 200xc2x0 F. (93xc2x0 C.) to 550xc2x0 F. (288xc2x0 C.), depending on type of composite. Press time may vary from 1 minute to 20 minutes duration.
Resin is applied to the treated plies, which are then formed with specific cross orientation of the veneers, or in the case of laminated veneer lumber all oriented in one direction. The formed billet is transferred into a press and consolidated into the final plywood or structural lumber substitute. Typical parameters include consolidation pressures ranging between 50 and 300 psi (between 35 and 198 N/cm2). Typical press temperatures may vary from 200xc2x0 F. (93xc2x0 C.) to 550xc2x0 F. (288xc2x0 C.). In some cases radio frequency curing may be utilized.
The physical and structural characteristics of the oil/copper ammonium acetate complex wood treatment treated composite or plywood panels are equivalent or superior in magnitude to similarly manufactured but untreated or copper ammonium acetate treated composites and plywood that are not treated with an oil.
Examples illustrating application of the invention using oriented strandboard and medium density fiberboard as the matrix are presented below.